Metcal MX-500P-11 Buzzing

[MrG]

Hey Folks,

My trusty (and used) Metcal buzzes since the day I got it. Even when the power switch on the unit itself is turned OFF. I'm assuming it's some Toroidal in the PSU, but wanted to get your input before I dive in.

To clarify, I am an intermediate repairperson, and am trying to bite off more and learn more in the process.

I bought a Hakko and it's ok, but I miss my Metcal so I'd like to get it repaired.

Thanks much,
MG

 

[moamps]

Does it work at all?

 

[MrG]

Works perfectly - it's just the perpetual buzz from the unit itself. It's pretty loud for a mechanical buzz.

 

[moamps]

Inside the power supply is actually a high power oscillator (transmitter ) that runs at 14MHz and is powered from a standard EI transformer. If the buzz is low frequency, then the cause is probably that transformer, but if the buzz is high frequency, then it probably comes from ferrite coils in the filter output stages. You can try gluing these coils a bit with some kind of fast glue, but be careful because any mechanical change can cause changes in the operation of this oscillator and lead to a decrease in the power of the soldering iron or stop working.

 

[MrG]

Wow, thanks very much. I’ll watch this a bit later today and investigate.

It is a low noise, like a 120hz thing if it we’re electrical. Is there a fix in mind for that?

thanks,
MG

 

[MrG]

Giving this a bump

 

[Arni]

It is probably the mains transformer. It is an EI core transformer. The power switch is a fairly complex electronic switch after the transformer, that's why it buzzing even when it is turned off. It is a very compact build, so it is difficult to fix. Maybe vacuum impregnating the transformer with epoxy, but you have to remove it from the PCB first. Or do as I do, get used to it. If I am not soldering, i disconnect it from the mains. When I am soldering, I just enjoy the bliss of a fantastic soldering station.

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